The proposed study is aimed at the analysis of control of gene expression during the transition from proliferating precursor cells to postmitotic differentiation during myogenesis. Myogenic cell line variants affected at specific stages of differentiation and cell lines derived from animals with hereditary diseases affecting the muscle tissue will be applied in the study. DNA probes complementary to specific RNA fractions will be used to analyze the changes in the synthesis, processing and activation of mRNA involved in differentiation.